The invention relates to a dielectric elastomer, i.e., stretchable dielectric elastomer film that on both faces is provided with electrode layers. The material of the dielectric elastomers according to the invention is constructed from, or by the use of, fluorosilicone polymers and has a greatly improved actuation elongation.
Dielectric elastomers are comprised of stretchable elastomer films that on both faces are coated with electrodes that are also stretchable. Upon elongation, the electrodes must maintain their electric conductivity. Such dielectric elastomers can be used as actuators, as sensors, or also as generators.
When used as an actuator, between the electrodes an electric potential is applied that causes the elastomer film, also referred to as dielectric, to be compressed with respect to thickness by the electrostatic pressure and, due to the approximate constant volume, to be expanded with regard to its surface area at the same time. In sensor operation the capacitance of the dielectric elastomer that is behaving like a flexible capacitor is measured. Upon elongation of the film, the capacitance of the capacitor changes so that elongations, forces or pressures can be determined. In operation as a generator, electric charges are transferred onto the expanded or stretched capacitor film. After relaxation of the stretched film, the charges are removed again at a higher energy state so that a gain in electric energy results.
The important properties for technical utilization of the elastomer material are the hardness or the modulus of elasticity, the electric breakdown field strength as well as the dielectric permittivity. The modulus of elasticity should be very minimal for many applications so that, for example, high actuator elongations in the electric field can be achieved in actuator operation. The electric breakdown field strength should be as high as possible in order to be able to apply high electric potentials and to thereby increase the actuation force and actuation elongation. Also, a high dielectric permittivity has a positive effect because the actuation force and actuation elongation are increased for identically applied electric field strength.
Known elastomer materials that are utilized as dielectric of dielectric elastomers are silicones (primarily polydimethylsiloxane), acrylates, polyurethanes, fluoropolymers, polybutadiene, natural rubber and others. With regard to suitable moduli of elasticity, for such materials a very broad range of 0.1 to 10 MPa, preferably of 0.3 to 3 MPa is proposed in U.S. 2007/0200467 A1. This publication mentions also a commercially available fluorosilicone without however dealing with its specific modulus of elasticity. The publications “Micro Electro Mechanical Systems” by R. Pelrine et al., 1997, pp. 238-243, and “Materials Science and Engineering” by R. Pelrine et al., C11, pp. 89-100 (2000) disclose that this material has a Young's modulus of 0.5 MPa but exhibits problems with regard to homogeneity of the material.
Electroactive polymer fibers for use as artificial muscles are disclosed in U.S. 2009/0085444 A1.
The present invention has the object to provide an improved material for the dielectric of a dielectric elastomer that in particular has a high permittivity and thus enables a high actuator elongation.